Purification of refrigerant



Dec. 24, 1940. R TAYLOR 2,225,669

PURIFICATION OF REFRIGERANT Filed May 25, 1939 FILTER CENTRIFUGE COOLER-CRYSTALLIZER REFRIG.

CENTRIFUGE Robe/*7 B. 7Iary/or- INVENTOR ATTORNEY Patented Dec. 24, 1940UNITED STATES PATENT OFFICE 2,225,669 PURIFICATION OF REFRIGERANT RobertB. Taylor, near Knoxville, Tenn. Application May 25, 1939, Serial No.275,701 11 Claims. (Cl. 62-124) (Granted under the act of March 3, 1883,as

amended April 30, 1928; 370 0. G. 757) The invention herein describedmay be manufood debris is, that upon continued contact of factured andused by or for the Government for the freezing medium with the frozenfood pargovernmental purposes without the payment to me ticles, anosmotic interchange takes place beof any royalty thereon. tween the cellcontents and the freezing medium.

This invention relates to the freezing of foods. The result of thisprocess is that upon approach- It is particularly directed to thepurification of ing osmotic equilibrium the cell contents of the liquidfreezing media used in the quick freezing of food particles no longerhave a freezing point foods by direct contact of the food with theliquid above that of the freezing medium and the parmedium at atemperature substantially below the ic es th w Out a d be o e At the m tfreezing point of the foods. the specific gravity of the food particlesbecomes 10 I have previously found that in the preservationapproximately the same as that of the freezing of foods by freezing twoessential conditions must medium so that the particles will not settleout of be maintained in order to preserve to the greatest the solution.Moreover, due to this substantially extent the natural characteristicsof the food. equivalent density of the particles and solution The foodshould not be subjected during the freezthere is no density differenceto be affected by the 15 ing process to a temperature substantiallylower separating forces of centrifugal separators. than the safe storagetemperature of the frozen I have now found, however, that when usingfood and the freezing operation should be effected aqueous solutions asa freezing medium, the puriso rapidly that only very small crystals areformed fication of the solutions may be effected in a very in thefoodstuff. simple and satisfactory manner. This is ac- 20 A particularlyeffective and successful method complished by lowering the temperatureof the for the quick freezing of foods which complies solution to apoint where crystals are formed with both of these conditions isdescribed in my and then subjecting the solution to centrifugalapplication Serial No. 91,442, filed July 18, 1936. separation. I havefound that when the con- 5 This method comprises directly contacting thetaminated solution is chilled until crystallization food, preferably inthe form of units having at begins, the crystals tend to form upon theconleast one dimension which does not exceed about taminating solidparticles as nuclei, thus formone inch, with an aqueous refrigerantsolution ing particles having asuiiiciently different density having afreezing point not higher than 0 F. and from the solution to permittheir separation from a low viscosity at 0 to 10 F. and which issuitable the solution by centrifuging. 30 for use in direct contact withfoods, maintaining This method of purification is particularly satthetemperature of the solution between the temisfactory and effective whenapplied to aqueous perature at which the food may be safely storedrefrigerant solutions of such composition that and a temperaturesubstantially below the freezupon lowering the temperature of thesolution ice ing point of the food, and circulating the solutioncrystals appear before crystals containing the 35 over the food at sucha rate that the temperature solute, that is, solutions which are on theice side of the solution adjacent the food remains below of the eutecticcomposition, as I have found that the freezing point of the food.Particularly adupon partial freezing of such solutions the icevantageous refrigerant solutions are provided by crystals do not form anadherent coating on the aqueous solutions of invert sugar which may, incooling surface but tend to remain suspended in 0 general, be used forthe freezing of fruit, vegethe solution.

tables and meats. Aqueous solutions of salts, par- It is, of course,desirable to carry the cooling ofticularly sodium chloride, may also beused, essuch aqueous refrigerant solutions only to the peciallyfor thefreezing of vegetables and meats. point where a small amount ofcrystallization has In the operation of freezing methods of theoccurred, the'formation of thick mushes being 5 7 type just described,it has been found that the avoided. This can readily be regulated byadrefrlgerant solutions tend to become contaminjusting the temperatureto which the solution is ated with food debris which is very difficultto cooled, so that the solution is cooled to a temper remove. Suchdebris, consisting principally of ature only slightly below thetemperature at fragments of the food being frozen, does not whichcrystallization begins.

readily settle out of the solution and neither filtra- This method isparticularly adapted to maintion nor centrifugal separation have beenfound tain the purity of aqueous refrigerant solueffective in removingthese contaminations. tions which initially have a predetermined freez-A principal reason for the difliculties which ing point. Either aportion of such solution may have been encountered in the removal ofsuch be removed directly from the zone of freezing in- 5 cooled to saidpredetermined freezing point whereby the water in such solution inexcess of e that required for the predetermined freezing point of thesolution separates as ice crystals associated with food debris. Afterseparating such crystals and the accompanying food debris the solutionso purified is returned to the zone of freezing. Under some conditionsitmay be desirable to cool the solution so removed to a temperatureslightly below said predetermined freezing point in order to removeadditional water so that the solution returned to the freezing zone mayhave a concentration such that when mixed with other aqueous refrigerantsolution entering the freezing zone said mixture will have substantiallysaid predetermined freezing point.

It is particularly advantageous to remove por tions of the freezingsolution from the main body thereof substantially continuously ratherthan to treat the whole body of the solution at separated intervals asby the continuous treatment of the solution many of the food particlesin the solution will not have arrived at the osmotic equilibriumreferred to above and their separation from the solution is'therebyfurther facilitated.

A desirable method of operation comprises cooling to the point ofpartial crystallization, and immediately centrifuging, the solutionremoved from the frozen food as it comes from the freezing apparatus andthereafter returning the purified solution to the freezing operation.

If necessary, suflicient water may be added to the purified solution tocompensate for the water removed as ice in the purification operation.Due to the fact that in the freezing operation the freezing solutiontends to become diluted by the absorption of water from the food beingtreated, it will be seen that this purification method also affords avery advantageous means for maintaining the desired concentration of thefreezing medium, as the addition of water to the purified solution canreadily be adjusted to maintain the solution at any predeterminedconcentration.

For the purpose of illustration, the invention will be more particularlydescribed with reference to the accompanying drawing which is adiagrammatic representation of a system of apparatus for freezing foodsembodying the principles of the present invention.

In the drawing, the comestible to be frozen is admitted through inlet Iof the freezing apparatus 3 and is withdrawn through outlet 5 afterpassing in direct contact with the aqueous refrigerant solution, whichmay, for example, be an aqueous solution of invert sugar containing 57%to 58% by weight of invert sugar and having a freezing point of 0 ismaintained at a proper temperature for freezing a comestible, forexample, between 4 F. and 10 F., by passing the same from the freezingapparatus 3 through conduit I, through the refrigerating machine 9 andreturning the same to freezing apparatus 3 through conduit H. The frozenfood withdrawn from the freezing appa-- ratus 3 is passed into acentrifuge l3 wherein substantially all the refrigerant solution isremoved from the frozen food. The refrigerant solution so removed fromthe frozen food, together with solid contaminants, is passed throughconduit I5 and through a heat exchange device or cooler I! wherein suchsolution is cooled by heat exchange with refrigerant to a temperature atwhich ice crystals form in the solution. When treating the thatrefrigerant solution which has been F. The refrigerant solution.

particular solution described above, it has been found suitable to coolthe solution to a temperature of 0 F., when it is desired to maintainsubstantially the original freezing point of the solution, or to atemperature below the aforestated freezing point temperature of theoriginal solution, such as 5 F., when it is desired to concentrate thesolution slightly above the original concentration before return to thebody of the refrigerant solution in the freezing apparatus. That portionof the refrigerant solution so cooled and containing ice crystals andassociated with solid contaminants in suspension is then passed throughconduit l9 and into filter centrifuge 2| wherein the ice crystals andthe accompanying solid contaminants carried by the solution are removedand the clarified and somewhat concentrated solution is then returned tothe body of the refrigerant solution through conduit 23. Similarly, aportion of the body of the refrigerant solution may be removed fromconduit I through conduit l5 and purified in the same manner as removedfrom the frozen comestible.

It will be seen, therefore, that this invention actually may be carriedout by the use of various modifications and changes without departingfrom its spirit and scope.

I claim:

l. A method of purifying aqueous refrigerant solutions contaminated withfood debris from direct contact with foods which comprises chilling thesolution until a relatively small amount of crystallization hasoccurred, and thereafter separating the crystals and accompanying debrisfrom the solution.

2. A method of purifying aqueous refrigerant solutions contaminated withfood debris from direct contact with foods which comprises chilling thesolution to a temperature a few degrees below the temperature ofincipient crystallization, and thereafter separating the crystals andaccompanying debris from the solution.

3. A method of purifying aqueous refrigerant solutions contaminated withfood debris from direct contact with foods which comprises chilling thesolution until a relatively small amount of crystallization hasoccurred, and thereafter separating the crystals and accompanying debrisfrom the solution by subjecting the partially crystallized solution tocentrifugal separation.

4. A method of purifying aqueous refrigerant solutions contaminated withfood debris from direct contact with foods which comprises chilling thesolution to a temperature a few degrees below the temperature ofincipient crystallization, and thereafter separating the crystalsandaccompanying debris from the solution by subjecting the partiallycrystallized solution to centrifugal separation.

5. A method of purifying aqueous refrigerant solutions containing morewater than corresponds to the eutectic composition and contaminated withfood debris from direct contact with foods which comprises chilling thesolution until a relatively small amount of ice crystals have formed,and thereafter separating the ice crystals and accompanying debris fromthe solution by subjecting the partially crystallized solution tocentrifugal separation.

6. A method of purifying aqueous refrigerant solutions containing morewater than corresponds to the eutectic composition and contaminated withfood debris from direct contact with foods which comprises chilling thesolution to a temperature a few degrees below the temperature thereofwith an aqueous refrigerant solution, the

improvement which comprises chilling the solution which has been removedfrom the food after the freezing operation to a temperature below thetemperature of incipient crystallization, thereafter separating thecrystals and accompanying food debris from the solution by subjectingthe partially crystallized solutionto centrifugal separation, and.returning the solution to the freezing operation.

8. In the freezing of foods by direct contact thereof with an aqueousrefrigerant solution, the improvement which comprises continuouslyremoving a portion of the solution from the zone of freezing, chillingthe solution so removed to a temperature below the temperature ofincipient crystallization, thereafter separating the crystals andaccompanying food debris from the solution by subjecting the partiallycrystallized solution to centrifugal separation, and returning thesolution to the zone of freezing.

9. In the freezing of foods by direct contact thereof with an aqueousrefrigerant solution, the improvement which comprises subjecting thefrozen food after the freezing operation to centrifugal force to removeadherent solution from the frozen food, chilling the separated solutionto a temperature below the temperature of incipient crystallization,thereafter separating the crystals and accompanying food debris from thesolution by subjecting the partially crystallized solution tocentrifugal separation, and returning the solution to the freezingoperation.

10. In the freezing of foods by direct contact thereof with an aqueousrefrigerant solution having a predetermined freezing point, theimprovement which comprisesremoving a portion of the solution from thezone of freezing, cooling the solution so removed to the temperaturecorresponding to said predetermined freezing point whereby the water insuch solution in excess of that required for the predetermined freezingpoint of the solution separates from the cooled solution as ice crystalsassociated with accompanying food debris, thereafter separating thecrystals and the accompanying food debris from the solution, andreturning the solution to the zone of freezing.

11. In the freezing of foods by direct contact thereof with an aqueousrefrigerant solution having a predetermined freezing point, theimprovement which comprises continuously removing a portion of thesolution from the zone of freezing, cooling the solution so removed tothe temperature corresponding to said predetermined freezing pointwhereby the water in such solution in excess of that required for thepredetermined freezing point of the solution separates from the cooledsolution as ice crystals associated with accompanying food debris,thereafter separating the crystals and the accompanying food debris fromthe solution, and returning the solution to the zone of freezing.

ROBERT B. TAYLOR.

